feelin

library6.2.0jsnpmunverified

Feelin is a robust JavaScript library designed to parse and interpret FEEL (Friendly Enough Expression Language) expressions, a standard defined by DMN (Decision Model and Notation). It provides functions like `evaluate` and `unaryTest` for executing FEEL expressions against a given context. The current stable version is 6.2.0, with minor releases and dependency updates occurring regularly, indicating active maintenance. Key differentiators include its comprehensive recognition of the full FEEL grammar, context-sensitive evaluation (handling names with spaces), built-in FEEL functions, and a focus on error recovery with detailed warnings for issues such as `null` conversions. While not yet fully DMN TCK compliant, it aims for high fidelity to the standard, making it suitable for integrating DMN decision logic into JavaScript applications.

serialization

npm install feelin

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · FEELIN

feelin

serializationjavascriptv6.2.0

Install

—

Import

—

Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

evaluate

✓ import { evaluate } from 'feelin';

✗ const { evaluate } = require('feelin');

Feelin is an ESM-first package, requiring Node.js >= 20.12.0 for direct usage. Use named imports.

unaryTest

✓ import { unaryTest } from 'feelin';

✗ import unaryTest from 'feelin';

Both `unaryTest` and `evaluate` are named exports, not default. Ensure correct destructuring.

✓ import * as feelin from 'feelin';

This pattern imports all named exports into a namespace object, useful for accessing multiple utilities without individual destructuring.

Demonstrates basic usage of `evaluate` and `unaryTest` functions, including context passing, list iteration, and inspecting `warnings` for execution issues like undefined variables.

import { evaluate, unaryTest } from 'feelin'; // Evaluate a simple expression with a context const result1 = evaluate("Mike's daughter.name", { 'Mike\'s daughter.name': 'Lisa' }); console.log('Expression evaluation:', result1.value); // Lisa // Perform a unary test const result2 = unaryTest('1', { '?': 1 }); console.log('Unary test 1:', result2.value); // true const result3 = unaryTest('[1..end]', { '?': 1, end: 10 }); console.log('Unary test 2:', result3.value); // true // Iterate and transform a list const result4 = evaluate('for a in [1, 2, 3] return a * 2'); console.log('Loop evaluation:', result4.value); // [2, 4, 6] // Check warnings for undefined variables or null conversions const { value, warnings } = evaluate('x'); console.log('Undefined variable result:', value); // null console.log('Warnings for undefined variable:', warnings); /* Output: [ { message: "Variable 'x' not found", type: 'NO_VARIABLE_FOUND', position: { from: 0, to: 1 } } ] */

Debug

Known issues

breakingStarting with v6.0.0, the package explicitly reports `null` conversion errors in the `warnings` array. Previously, such errors might have been silently handled or returned `null` without explicit warning details. Developers should now inspect the `warnings` property of the result object to understand why a `null` value was produced.

fix

Always check the `warnings` array in the returned object for detailed error information, especially when `value` is `null`. Adapt any logic that relied on implicit `null` handling to explicitly process these warnings.

affects: >=6.0.0

gotchaFeelin requires Node.js version 20.12.0 or higher. Using it with older Node.js versions may lead to compatibility issues, particularly with ESM imports or underlying dependencies.

fix

Ensure your Node.js environment meets the minimum requirement of 20.12.0. Update Node.js if necessary.

affects: <20.12.0

gotchaThe package is primarily designed as an ES module (ESM). Attempting to use `require()` for imports in a CommonJS environment without proper transpilation or configuration will result in an error.

fix

For Node.js environments, use `import { evaluate } from 'feelin';` in ES module contexts. If you must use CommonJS, consider dynamic `import()` or ensuring your build setup transpiles ESM to CJS.

affects: all

gotchaWhile `feelin` recognizes the full FEEL grammar and includes many built-in functions, it is not yet fully compliant with the DMN TCK (Decision Model and Notation Test Compatibility Kit). This means certain complex or edge-case FEEL expressions might behave differently compared to a fully TCK-compliant engine.

fix

Consult the project's DMN TCK coverage documentation (e.g., `./docs/DMN_TCK.md` in the repository) to understand current limitations and ensure critical DMN expressions function as expected in your specific use case. File issues for observed discrepancies.

affects: all

Errors

Common errors & fixes

TypeError: require is not a function

Attempting to import `feelin` using CommonJS `require()` syntax in an ES module context or without proper CommonJS fallback/transpilation.

fix

Use ES module import syntax: `import { evaluate } from 'feelin';` in your JavaScript/TypeScript files. Ensure your project is configured for ES modules (e.g., `"type": "module"` in `package.json`).

Variable 'x' not found

An expression references a variable (e.g., 'x') that is not present in the provided context object.

fix

Ensure all variables referenced within your FEEL expression are provided as properties of the context object passed to `evaluate` or `unaryTest`. For example, `evaluate('x', { x: 10 })`.

Upgrade

Version history

6.2.0latest on npm

Audit

Dependencies

lezer-feelrequiredCore dependency providing the FEEL language definition for parsing.

@lezer/commonrequiredUnderlying Lezer parser system component.

Agent activity

8 hits · last 30 days

node

Resources

githubhttps://github.com/nikku/feelin ↗

packagehttps://www.npmjs.com/package/feelin ↗

homepagehttps://feelintheloupe.github.io/feelin/ ↗